1. Field of the Invention
This invention relates to a process for preparing polybutadiene using a catalyst having high activity in stereoregularity and in conversion, and more particularly, to the process for preparing polybutadiene with high 1,4-cis content over 97% and high conversion over 90% in such a manner that 1,3-butadiene is polymerized using a catalyst prepared by aging a mixture of neodymium compound, organoaluminum compound and borontrifluoride complex in the presence or absence of a small portion of conjugated diene compound.
2. Description of the Prior Art
When polybutadiene is intended to be prepared via polymerization of 1,3-butadiene, the method of using lanthanum series metal catalyst, i.e., the elements from atom number 57 (La) to 71 (Lu), can provide diene polymer containing higher 1,4-cis content than other methods which comprise polymerizing one or more of conjugated diene in the presence of transition metal compound such as nickel (Ni), titanium (Ti) and cobalt (Co).
Among lanthanum series metals, cerium (Ce), lanthanum (La), neodymium (Nd) and gadolinium (Gd) are known to have an excellent catalytic activity; among them, neodymium has the most excellent catalytic activity.
The preparations of high 1,4-cis polybutadiene(hereinafter referred to as "high cis-BR") in the known methods containing a lanthanum series metal catalyst are as follows: The PCT No. 93-05083 has disclosed a process for the preparation of "high cis-BR" using a catalyst prepared by mixing (a) neodymium compound, (b) silicon halide or organosilicon halide, (c) organoaluminum compound and (d) diene compound, and then aging;
The U.S. Pat. Nos. 4,906,706 and 5,064,910 have disclosed a process for the polymerization of 1,3-butadiene using a catalyst which is prepared by aging a mixture of a rare earth metal, a Lewis acid and/or a Lewis base and an organoaluminum compound in the presence or absence of diene compounds. Also, the improvement of the physical properties of the resulting polybutadiene has been achieved by treating it with a modifying compound selected from the group consisting of an isocyanate, a carbon disulfide, an epoxy compound and an organotin halide compound;
The U.S. Pat. No. 4,699,962 has disclosed a process for the preparation of "high cis-BR" using a catalyst comprising a neodymium hydride, a chlorine-donor compound, an electron donor ligand and an organoaluminum compound;
The European Pat. No. 127,236 has disclosed a process for the polymerization of 1,3-butadiene using a catalyst containing (a) a neodymium compound, (b) an organohalide compound, (c) an organic compound having a hydroxy group and (d) an organoaluminum compound;
The European Pat. No. 375,421 and the U.S. Pat. No. 5,017,539 have disclosed a process for the preparation of "high cis-BR" using a catalyst comprising (a) a neodymium compound, (b) an organohalide compound and (c) an organoaluminum compound;
The European Pat. No. 667,357 has disclosed a process for preparing "high cis-BR" using a catalyst which is prepared by aging a mixture of a neodymium compound, an organoaluminum compound and tris(pentafluorophenyl)boron compound in the presence or absence of diene compound.
But, the known techniques have the following problems; (a) preparing of polybutadiene with high yield and high 1,4-cis content is difficult, (b) some gellation is caused due to the heterogeneity of catalyst in non-polar solvent.
Further, solution polymerization of diene monomer using a heterogeneous catalyst system, forming suspended matter due to incomplete dissolution to non-polar solvent, comparing to solution polymerization using a homogeneous catalyst system, usually produces some gel. The resulting gel causes increasing solution viscosity of the polymer as well as inhibiting flow of reactant or product due to accumulating of the gel at the wall of the reactor or pipe line. In addition, a heterogeneous catalyst system, comparing to a homogeneous catalyst one, gives some difficulty in controlling the amount of catalyst quantitatively which is essentially needed for smooth polymerization and for easy control of the physical properties of polybutadiene.